The invention relates to a one-way clutch, and more particularly, to a one-way clutch which prevents sprags from sinking into pockets of a retainer and achieves a stable engagement characteristic, by means of a protuberance formed at an edge of each pocket of a retainer so as to protrude in a radially outward direction.
As shown in FIG. 12, a one-way clutch employed in an automatic power transmission system of an automobile usually comprises a retainer 13, a spring 14, and sprags 15. The one-way clutch is disposed in an annular space 20 defined between an outer ring 11 and an inner ring 12. By means of relative rotation arising between the outer ring 11 and the inner ring 12, the inner and outer rings are subjected to repeated rotation and locking. Specifically, when the sprags 15 are rotated in one direction, the sprags 15 act as wedges, whereby the outer ring 11 and the inner ring 12 rotate in an integrated fashion (locked state), thus transmitting power. When the sprags 15 are rotated in the opposite direction, the sprags 15 perform idle running, thus interrupting power transmission (i.e., an unlocked state). The one-way clutch which repeatedly performs transmission and interruption of power requires synchronism between sprags"" operations and appropriate engagement at all times. For this reason, considerable thought has been put into measures for preventing another member from hindering operations of the sprags. Further, the one-way clutch of sprag type can achieve a stable engagement characteristic for the sprags even when variations attributed to misalignment have arisen between inner and outer bearing rings.
In such a one-way clutch of sprag type, the spring 14 is guided along the inner radius side of the retainer 13, thereby accurately positioning, in a radial direction, the sprags 15 held by the retainer 13 and the spring 14. Tongue-like flaps 14t of the spring 14 usually impart pre-stress (force) to the sprags 15 in a direction in which the sprags 15 are to be locked, thus contributing to an engagement characteristic. As mentioned, in relation to the one-way clutch, every time idle running and engagement of the sprags 15 are repeated, an outer peripheral cam surface 15a of each sprag 15 rotates over an inner peripheral surface (raceway surface) 11a of the outer ring 11, and an inner peripheral cam surface 15b rotates over an outer peripheral surface (raceway surface) 12a of the inner ring 12.
In some cases, a one-way clutch of sprag type experiences slippage for reasons of misalignment, vibration, or decentering between the outer and inner rings during the course of pivotal movement in which sprags shift from a free rotation state to a locked state and vice versa, As shown FIG. 11, when slippage has arisen, torque is imparted to each sprag 15 while an edge Q of each pocket 13p of the retainer 13 is taken as a fulcrum. At this time, a recess 5c of the sprag 15 overlaps the edge Q of the pocket 13p of the retainer 13. The sprag 15 rotates in the direction of arrow Z while the point Q is taken as a fulcrum. If the pocket 13p of the retainer 13 is large, there arises a problem or a protuberance id formed at an upper edge of the sprag 15 sinking in toward the inner radius side of the pocket 13p. If such a sinking phenomenon arises, ensuring synchronism between sprags becomes difficult, thereby adversely affecting engagement performance of the clutch. However, each of the pockets 13p of the retainer 13 must have a predetermined minimum length for ensuring smooth action of the sprag 15.
The one-way clutch such as that shown in FIG. 12 is constituted of a retainer 23, a spring 14 guided by the retainer, and sprags 15 fitted into pockets 13p of the retainer 13 and pockets 14p of the spring 14. The one-way clutch is placed in an annular space defined between an unillustrated outer ring and an unillustrated inner ring. In such a one-way clutch, tongue-like flaps 14t of the spring 14 usually impart pre-stress (force) to the sprags 15 toward a direction in which the sprags 15 are to be locked, thus contributing to an engagement characteristic, and support the respective sprags 15 at all times. The one-way clutch is conveyed or transported while the retainer 13, the spring 14, and the sprags 15 are built together. The one-way clutch is incorporated into a space between an outer ring and an inner ring at a location where an automatic power transmission system is to be built.
As mentioned above, before being incorporated into a space between an outer ring and an inner ring, the one-way clutch is transported while a retainer, a spring, and sprags are built together. The sprags are merely held by tongue-like flaps formed in a spring guided along an inner radius side of the retainer. Retaining force (supporting force) of the tongue-like flaps of the spring substantially fails to act on the sprags before the clutch is incorporated into a space between an outer ring and an inner ring. In other words, the sprags are in a so-called free state. Accordingly, there has been a problem of sprags readily dropping from pockets of a spring (or pockets of a retainer) when subjected to slight external force during, e.g., transport.
Every time idle running and engagement of the sprags 15 are repeated, an outer peripheral cam surface 15a of each sprag 15 rotates over an inner peripheral surface (raceway surface) 11a of the outer ring 11, and an inner peripheral cam surface 15b rotates over an outer peripheral surface (raceway surface) 12a of the inner ring 12. Such a one-way clutch which repeatedly performs transmission and interruption of power requires synchronous actions and appropriate engagement of sprags at all times. Hence, considerable thought is put into preventing another member from hindering the actions of the sprags.
In some cases, a one-way clutch of sprag type experiences slippage for reasons of misalignment, vibration, or decentering between outer and inner rings during the course of a pivotal movement process in which sprags shift from a free rotation state to a locked state and vice versa. As shown FIG. 11, when slippage has arisen, torque is imparted to each sprag 15 while an edge Q of each pocket 3p of the retainer 13 is taken as a fulcrum. At this time, a recess 15c of the sprag 14 overlaps the edge Q of the pocket 13p of the retainer 13. The sprag 15 rotates in the direction of arrow Z while the point Q is taken as a fulcrum. If the pocket 13p of the retainer 13 is large, there arises a problem of a protuberance 15d formed at an upper edge of the sprag 15 sinking (falling) in toward the inner radius side of the pocket 13p, as designated by a chain double-dashed line. If such a sinking phenomenon arises, the sprag fails to return to its original engagement position, thus failing to ensure synchronism and adversely affecting engagement performance of the clutch. Alternatively, the retainer 3 may be damaged. However, each of the pockets 13p of the retainer 13 is required to have a predetermined length for ensuring smooth action of the sprag 15.
The invention has been conceived to solve the problem and object of the present invention is to provide one-way clutch which prevents dropping of sprags from pockets even when subjected to external force during transport and which involves a simple assembly operation.
Another object of the invention is to provide a one-way clutch which ensures a required length for pockets of a retainer and prevents an upper end of each sprag from sinking into a corresponding pocket even when the sprag has experienced slippage and torque.
Another object of the invention is to provide a one-way clutch in which an upper end of a sprag does not sink into a corresponding pocket of a retainer even when the sprag experiences slippage, to thereby generate torque.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A one-way clutch comprising:
a retainer in including a pocket;
a spring which includes a pocket and a tongue-like flap and is guided by the retainer; and
a sprag which is pivotally provided in the pockets of the retainer and the spring, and forced by the tongue-like flap in a direction in which the sprag is to be locked, respectively, wherein a maximum circumferential width of an outer cam surface of the sprag and a maximum circumferential width of an inner cam surface of the sprag are greater than a circumferential width of the pocket of the retainer, and the sprag has a width of the sprag in a direction of inclination which is made smaller than the circumferential width of the pocket of the retainer.
(2) The one-way clutch according to (1), wherein the width of sprag in the direction of inclination corresponds to a width across flat.
(3) A one-way clutch placed in an annular space between an outer ring and an inner ring comprising:
a retainer including a pocket;
a spring which includes a pocket and a tongue-like flap guided by the retainer; and
a sprag which is fitted into pockets of the retainer of the spring and are forced, by tongue-like flaps formed in the spring, toward a direction in which the sprag is to be locked; and
a protuberance radially outwardly protruding from an edge on a part of the pocket of the retainer facing a direction in which the sprag is to be unlocked.
(4) The one-way clutch according to (3), wherein a plurality of the protuberances protrudes from the edge of the pocket.
(5) The one-way clutch according to (3), wherein the sprag comes into contact with the protuberance to prevent the sprag from sinking into an inner radius side of the pockets.
(6) The one-way clutch according to (3), wherein the protuberance comes into contact with the sprag when the sprag released from a locked state and freely rotates.
(7) A one-way clutch placed in an annular space between an outer ring and an inner ring comprising:
a retainer including a pocket;
a spring which includes a pocket and a tongue-like flap guided by the retainer; and
a sprag which is fitted into pockets of the retainer of the spring and are forced, by tongue-like flaps formed in the spring, toward a direction in which the sprag is to be locked;
a recess, for a pivotal movement of the sprag when the sprag pivots in an unlock direction in which the sprag is to be released from a locked state, formed in the sprag; and
a projection formed at a part of an outer cam surface of the sprag which faces the unlock direction,
wherein a position on the recess at which the recess comes into contact with an edge of the pocket of the retainer is taken as a fulcrum, and a distance between the fulcrum and a surface of the projection is set to become longer than a circumferential length of the pocket of the retainer.
(8) The one-way clutch according to (7), wherein the projection comes into contact with the pocket of the retainer to prevent the sprag from sinking into an inner radius side of the pockets.